oxc-project/oxc · error

Read-only global '{global_name}' should not be modified.

Error message

Read-only global '{global_name}' should not be modified.

What it means

Diagnostic from oxlint's no-global-assign rule (ESLint port, eslint:recommended). It fires when an assignment writes to a read-only global: a built-in like undefined, NaN, or Infinity, or any variable your lint globals config marks readonly. Such writes throw a TypeError in strict mode or silently no-op in sloppy mode, so the rule stops them statically. The rule config accepts a list of global names to exclude.

Source

Thrown at crates/oxc_linter/src/rules/eslint/no_global_assign.rs:15

use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::Span;
use oxc_str::CompactStr;
use schemars::JsonSchema;
use serde::Deserialize;

use crate::{
    config::GlobalValue,
    context::LintContext,
    rule::{DefaultRuleConfig, Rule},
};

fn no_global_assign_diagnostic(global_name: &str, span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn(format!("Read-only global '{global_name}' should not be modified."))
        .with_help(format!("Use a local variable instead of modifying the global '{global_name}'."))
        .with_label(span.label(format!("Read-only global '{global_name}' should not be modified.")))
}

#[derive(Debug, Default, Clone, Deserialize)]
pub struct NoGlobalAssign(Box<NoGlobalAssignConfig>);

#[derive(Debug, Default, Clone, JsonSchema, Deserialize)]
#[serde(rename_all = "camelCase", default, deny_unknown_fields)]
pub struct NoGlobalAssignConfig {
    /// List of global variable names to exclude from this rule.
    /// Globals listed here can be assigned to without triggering warnings.
    exceptions: Vec<CompactStr>,
}

impl std::ops::Deref for NoGlobalAssign {
    type Target = NoGlobalAssignConfig;

View on GitHub (pinned to e1e7af627c)

Solutions

1. Use a fresh local variable instead of writing to the global.
2. If the global genuinely should be writable in your environment, declare it writable in the lint globals config.
3. Add the name to this rule's exceptions list in .oxlintrc.json.
4. Delete pre-ES5 undefined guards; the property is non-writable in modern engines.

Example fix

// before
undefined = null; // silent no-op, TypeError in modules

// after
const missing = null;

const readonlyWrite = /\b(?:undefined|NaN|Infinity)\s*=[^=]/.test(source);

When it happens

Trigger: undefined = 5; or NaN = NaN + 1;; writing to a global declared readonly in the globals section of .oxlintrc.json; assigning to built-ins like Infinity inside math helpers.

Common situations: Legacy browser scripts using undefined as a storable variable; pre-ES5 copied code that 'guarded' undefined; shared lint configs marking environment globals readonly, causing false positives in files that legitimately shadow them.

Related errors

• Unexpected assignment to read-only global variable.
• Empty array binding pattern
• Empty object binding pattern
• Redundant Boolean call
• This label '{label_name}' is unnecessary

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/4588c5a09592b097. Report an issue: GitHub.